In recent years, driver's condition detecting devices have been proposed. For example, consider a first related technology (JP2003-80969A). The first related technology is concerned with the frequency at which a driver's direction of a look (or, in other words, viewing angle) changes. The driver's condition (or, in other words, quality) of alertness is determined based on the measured frequency.
As another example, consider a second related technology (JP2002-25000A). According to the second related technology, visual recognition time, reaction time, the number of times that visual recognition occurs, the number of times of look holding (i.e., that a look is held), etc. are detected as indicators of a driver's condition of alertness. The visual recognition time refers to the total time elapsed while a driver looked at a given subject, e.g., a spot on an information display screen. Reaction time refers to the time until the driver reacts to a visual stimulus. The number of times of visual recognition refers to the number of instances that a driver looked at a recurring visual stimulus. The number of times of look holding refers to the number of instances that an elapsed amount of time during which the driver gazed continuously at a persistent visual stimulus equaled or exceeded a threshold duration. The second related technology judges a driver's condition based on these detected parameters.
The first related technology mentioned above only detects a driver's direction of a look. Consequently, it is difficult to distinguish between a driver's intentional visual recognition and a coincidental look mistaken as a visual recognition. Coincidental looks can skew the assessment of the driver's condition, both positively and negatively.
The second related technology detects a driver's visual recognition of a visual stimulus whose position on the display screen is static. As such, it is difficult to assess, e.g., how well the driver can recognize an object that would jump into the driver's field of view.